Energy-efficient general lighting with good color rendering is presently provided by gas discharge lamps such as fluorescent, high pressure sodium and metal halide. These lamps achieve energy efficiencies in the range of 60 lumens per watt (lpw) to 110 lpw depending on the power level and other particular features. These lamps are much more efficacious than the common incandescent lamp which at best, with added infrared coatings, can achieve 35 lpw, but are more typically in the range of 15 lpw. Presently, the above listed gas discharge lamps typically use the element mercury, a toxic substance, as a key material for efficient light production.
On May 14, 1992, PCT Publication Number WO 92/08240 entitled "HIGH POWER LAMP" and on Oct. 28, 1993, PCT Publication WO 93/21655 entitled "LAMP HAVING CONTROLLABLE CHARACTERISTICS" (both of which are incorporated herein by reference) were published in which a new mercury-free lamp with excellent color-rendering properties was disclosed. That lamp discussed is capable of producing visible light efficiently at high powers (in the KW range) with the use of environmentally benign sulfur or selenium containing substances including elemental sulfur, elemental selenium or compounds of those elements as the light emitter and is powered by a magnetron operating at microwave frequencies (.apprxeq.2.25 GHz). The light producing material (sulfur) along with a back fill of inert gas (argon) are contained in a rotatable, small transparent quartz spherical bulb. The reason for the potential of high efficiency and good coloring rendering are that the emitted radiation is essentially continuous broad band spectrum confined mostly to the visible wavelength region.
It would be advantageous to have the greater efficiencies of a sulfur lamp for general lighting applications, including those which operate at low power (under 200 watts). To do so several major and significant technical problems which are exhibited by the prior art need to be solved. The most significant of those problems are:
1. Operation of the sulfur lamp at low power, i.e. 50w/cc and above; PA1 2. Operation of the sulfur lamp at RF frequencies (&lt;1 Ghz) where present day understanding of low power electronic power supplies predict very efficient possibilities (.apprxeq.90%); and PA1 3. Development of a coupling mechanism whereby the RF power can be efficiently transferred into the sulfur lamp allowing achievement of luminous efficiencies of at least 150 lumens per RF watt.
The present invention provides such a lamp system.